Hydrothermal synthesis of sodium titanate nanosheets using a supercritical flow reaction system

Abstract

Sodium titanate (NTO) nanosheets were directly synthesized in supercritical water using a flow hydrothermal reaction system (FHRS) from Ti-sols and NaOH solutions. The syntheses were carried out at temperatures from 350 to 410°C, at pressure of 30 MPa, for reaction times from 0.25 to 0.67 s, and initial Na/Ti molar ratio of 2.5 to 10. X-ray diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM), BET surface area, TGDTA analyses, and Dynamic light scattering (DLS) techniques were used to characterize the samples. Single phase of NTO was achieved under supercritical conditions (>400°C) at initial Na/Ti molar ratio>5. The NTO nanosheets have lateral dimension in the range of approximately several submicrons and thickness in the order of nanometers which are stacked nanosheets with 4070m2/ g of specific surface area. Hydrogen ion-exchange and tetrapropylammonium intercalation properties of NTO synthesized by FHRS were compared with those of solid-state reacted NTO. Intercalation of tetrapropylammonium ions into FHRS NTO can readily occur due to enlargement of interlayer spacing after hydrogen-ion exchange whereas it did not take place on the solid-state reacted NTO owing to the shrinkage of interlayer spacing after hydrogen-ion exchange.